The invention relates to weathering-resistant pearlescent pigments based on mica flakes coated with metal oxides.
Pearlescent pigments based on mica platelets coated with metal oxides are used in many industrial fields, such as, for example, in cosmetics, namely as pigments for nail varnishes, lipsticks, powders and the like, but also for pigmenting plastics and paints of any kind. However, in particular if these pigments are incorporated into organic polymers, for example if they are used in paints, inks and plastics, it is observed that the weathering resistance of the polymers is impaired by the presence of pearlescent pigment. It is evidently the case that the combined action of natural light, having a high UV content, and of moisture is catalyzed by the metal oxides applied to the mica platelets and causes rapid decomposition of the polymer matrix.
It is known from German Offenlegungsschrift No. 2,215,191 to coat such pigments with an additional coating of methacrylatochromium chloride. This has the effect of achieving good weathering resistance in coating films or plastics. However, if the pigments are coated with effective levels of this chromium complex, the strong green self-color of the additional coating is found to be disadvantageous to the gloss and the coloring quality of the pigment. Moreover, chromium-based coatings are undesirable for various applications, such as, for example, food packaging.